Issue 22: Switch to Go modules

[johandry]

Changes done:

• Update Go modules
• Migrate to Go 1.13.1

What was done:

# Use a new GOPATH
export GOPATH=$(mktemp -d)

# Update the Go modules
go mod tidy

# Make all
make all

How to test:
The build and all the validations done with make all are done without error.

Comments:
There was a go.mod file not updated so I think the migration to Go modules was previously done. I just update the latest modules and set Go 1.13 because there are some improvements and security fixes.

[CLAassistant]

All committers have signed the CLA.